The present invention relates to an arc welder and more particularly, the present invention firstly relates to a rectifier phase control type arc welder and more specifically to an arc welder which can fully contribute to the reduction of the number of components of a welder control circuit and a manufacturing cost thereof, the enhancement of performance of the welder, operability on a part of users and the feasibility of change of functions.
Secondly, the present invention relates to an arc welder in which welding condition setting signals determined in a welding process are stored and they are subsequently read out selectively to carry out the welding process.
Thirdly, the present invention relates to an arc welder in which an output voltage or an arc voltage and a welding current are controlled in unison or individually, and in the in-unison control mode an optimum output voltage or arc voltage and welding current relationship is continuously maintained to attain stable welding.
Regarding the first point, a prior art D.C. arc welder of the SCR firing phase control type has a disadvantage that the number of components of the control circuit is large. For example, the firing phase control circuits are provided one for each of the SCR's. Accordingly, it is troublesome to determine whether desired conditions are met. In addition, since it is based on analog control, automation of production of the circuits such as by IC circuits or LSI circuits is hard to attain and a manufacturing cost is high. From the view points of change of functions of the welding sequence and the enhancement of performance, the prior art system which is based on the analog control is not easy to change design or, if not impossible, a problem of price is encountered. Moreover, the circuits are utilized in the welding environment and are, therefore, subject to damage from, for example, heat generated during welding. The prior art system also did not provide sufficient protection with respect to the damage of the control circuit due to malfunctions of the control components.
Regarding the second point, it has been difficult in the past to determine the welding conditions suited for a particular article to be welded in known welding methods such as arc welding or resistor welding, and a considerable level of knowledge and experience were needed. For example, in a semi-automatic gas shield arc welding in which a consumable electrode is continuously fed to attain high efficiency welding, a welding current and a welding voltage are specifically determined by the experience and knowledge of a welding operator although general conditions of process are known for particular objects to be welded. Accordingly, it is difficult for an unexperienced operator to carry out the welding process. Furthermore, where the process is carried out under at least two process conditions, control elements for one process condition, which has once been met properly, has to be changed in order to meet the other process condition, and the conditions must be checked for their properness by a test arc whenever the conditions are changed. Even where a single process condition is used, if a control element such as a potentiometer is moved inadvertently, the original proper condition is lost.
In addition, the control element is preset to a position which is expected to meet the desired process condition, but whether it is a proper position or not is determined only after a welding power has been actually fed. In other words, whether the presetting is proper or not cannot be determined until welding occurs. Furthermore, since the adjustment is carried out using marking such as a scale or digits on a control panel of the control element, precision of setting is poor and the adjustment is difficult to attain. In the apparatus such as the semi-automatic gas shield arc welder described above in which the welding process conditions are determined by setting the welding voltage and the feed rate of the consumable electrode, if the process is started without having exactly set the control elements, a hole is formed in the article to be welded, defect beads are formed, or the welder is damaged or the lifetime thereof is shortened.
To resolve the above problems, it has been proposed to automate the setting of the welding conditions which were set in the past by the operator for each of the welding processes. In one proposed method, initial condition setting signals for welding and event signals (such as actual welding voltage and welding current) desired from the welding process carried out in accordance with the initial conditions are stored in storage means, and when the next welding process is to be initiated the initial condition setting signals are read from the storage means to start the welding process based on those signals, and after a predetermined time period has elapsed, the event signals are read from the storage means which are then used as the welding condition signals and the process are controlled to meet those conditions. (See Japanese Patent Publication No. 40182/73). However, in many cases, whether the settings are proper or not cannot be determined until after the welding process has actually been carried out, and the preset conditions are usually modified during the welding process. Accordingly, where the initial condition setting signals and the event signals stored are subsequently used on the assumption that they are correct, proper welding may not be attained. In addition, since the event signals in the welding period are all to be stored, a large capacity of storage means is required, and read and write operations to the storage means have to take place almost continuously.
Finally, regarding the third point discussed above, the prior art union/individual control circuit comprises a group of resistors. In order to generate an exact SCR firing reference voltage V.sub.BV for an arc voltage for a particular wire diameter based on an SCR firing reference voltage V.sub.BM of a wire feeding motor in the union control mode, high precision resistors are needed. However, the characteristics of the resistors change by temperature change which temperature changs are prevalant in a welding environment. Therefore, high precision is not attained in the union control mode. In addition, a compensation circuit for voltage fluctuation is not satisfactory although it is provided. A relation between the welding current and the welding voltage is non-linear and it is difficult to develop a proper relation by resistors. Furthermore, since the resistors are needed one for each of the wires of different diameters, the number of components is large, and the adjustment and the test for the potentiometers when the welder is shipped are troublesome. The operability is also poor.